Many commercially available electronic devices for communication, data processing, automatic control, aviation systems, space systems and the like require power in the form of a substantially constant voltage which can be supplied from a battery or through a regulated or unregulated power supply, often referred to as a voltage converter or power converter. While analog voltage regulator circuits have long been known, they are generally of low efficiency when significant currents are delivered since a voltage drop necessarily occurs across them, consuming power which must then be dissipated, generally as heat.
To improve efficiency, numerous switched power converter/inverter and voltage regulator topologies have been developed in recent years which use switches to intermittently provide power (which may or may not be smoothed by circuits including one or more inductors) to one or more filter stages, generally embodied with capacitors which can reduce ripple voltage magnitude to acceptable levels. Switched or switching power supplies are more efficient than analog voltage regulators since only nominal voltages are developed across the switches when conductive and only small or negligible currents are carried by the switches when nominally non-conductive. The voltage can be regulated over a wide range of voltages and load currents by varying the switching frequency or duty cycle of the input power.
However, in switched power supplies, to limit ripple voltage and to accommodate potentially large load transients, switching frequencies are generally high; usually in the range of several hundred KHz to several MHZ. Therefore, current and, sometimes, voltage transients may be large, particularly where the load current is high and/or where the voltage difference from input to output of the switched voltage regulator is large. Accordingly, switched voltage regulators can generate significant amounts of electromagnetic interference (EMI) noise having both common mode (CM) and differential mode (DM) components which may be radiated and/or reflected to the input and ultimately to the power source which may be the public power distribution grid from which it may be transmitted or conducted to other similarly connected devices. Therefore, the magnitude of EMI noise generated by a switched power supply (and any load connected to it) must be minimized and regulated to acceptably low levels, usually by the application of filters.
For high power applications, multi-phase power supplies have become very popular since the required load current can be satisfied by respective switched power supplies of a plurality of overlapping phases such that current requirements of any single phase can be reduced (and the cost of components thereof reduced accordingly). However, because of the high currents, large current ripples, high dv/dt and large parasitic parameters in multi-phase power electronics systems, the EMI noise is difficult to control. The size of the EMI filters which must be applied to each respective phase can be significant and may constitute up to half the volume of the entire power electronics system. Conventionally, EMI noise for a single phase AC or DC power supply can be substantially decoupled into its CM and DM components and CM and DM filters applied to suppress the CM and DM noise, respectively, once the characteristics (e.g. magnitude and spectrum) of the CM and DM noise are known. One approach to optimizing filter design so that the physical size of the filter can be minimized would ordinarily be to design the filter(s) based on measured EMI noise. However, conventional measurement methods cannot differentiate between CM and DM noise components. Therefore, conventional EMI noise measurements do not provide sufficiently accurate data to be effective for optimal filter design. Further, while a technique for separating DM and CM components of EMI noise for a single-phase voltage converter or power supply has been developed, separation of CM and DM noise components is very much more difficult and complex for a multi-phase application due to potential imbalance between phases and coupling and other interactions between phases that are electrically connected, at least at the common input power source. To date, no technique or circuit exists for separating CM and DM EMI noise components to provide sufficiently independent measurement of CM and DM noise components in a multi-phase application or for a device operating from multi-phase AC or DC power supplies to support optimal EMI noise filter design.